Millennial Media (MM+8.1%) surges after Oppenheimer's Jason Helfstein predicts the mobile ad network owner will report solid Q4 results on Tuesday, and states his research indicates Millennial will face limited mobile ad competition in the near-term (ed: Google's AdMob seems a formidable rival). Helfstein, who smartly made a bullish call on Millennial ahead of its Q2 report, also notes the company's very high short interest (45.5% of the float was shorted as of Jan. 31).